Spectral sensitivity and retinal pigment movement in the crab Leptograpsus variegatus (fabricius)

1. The retina of Leptograpsus contains five types of movable screening pigment. The positions of these were found under various conditions of illumination in the day and at night. 2. Intracellular recordings were made of the spectral responses of retinula cells R1-7 under the same conditions, with the eye in situ. 3. The spectral absorptions of the individual screening pigments were measured by ultramicrospectrophotometry. 4. Calculations based on a simple model of screening pigment action suggest that the observed variation in spectral sensitivity with light and dark adaptaton may be largely explicable in terms of the effects of these screening pigments on a rhodopsin of peak absorbance at 485 nm. 5. Light-adapted angular sensitivities are comparable to those of insects with high acuity apposition eyes.